Apoptosis is the process by which a cell actively commits suicide through a tightly controlled program (See for example, Wyllie A H, et al., 1980, Cell death: the significance of apoptosis. Int Rev Cytol 68:251-306). Morphologically, apoptosis is characterized by shrinkage of the cell, dramatic reorganization of the nucleus, active membrane blebbing, and ultimately fragmentation of the cell into membrane-enclosed vesicles (apoptotic bodies) (Earnshaw W C, 1995, Nuclear changes in apoptosis. Curr Opin Cell Biol 7:337-43). Apoptosis occurs in two physiological stages: commitment and execution.
Recent experiments have demonstrated that mitochondria play an essential role in apoptotic commitment (Green D R et al., 1998, Mitochondria and apoptosis. Science 281:1309-12). Upon apoptotic stimulation, several important events occur at the mitochondria, including the release of cytochrome C. Release of cytochrome C from the mitochondria can be inhibited by the expression of anti-apoptotic Bcl-2 family members (such as Bcl-2 and Bcl-XL) and induced by the expression of pro-apoptotic Bcl-2 proteins (such as Bax and BID). During receptor-mediated apoptosis, BID is cleaved at its N-terminus by caspase-8. The carboxyl-terminal fragment of BID (MW 15 kDa) is then inserted into the membrane of the mitochondria, triggering release of mitochondrial cytochrome C (Li H, et al., 1998, Cleavage of BID by caspase-8 mediates the mitochondrial damage in the Fas pathway of apoptosis. Cell 94:491-501).
Releasing cytochrome C from mitochondria commits the cell to die by either apoptosis or necrosis. The cytochrome C-induced apoptotic process involves Apaf-1-mediated caspase activation. This cytosolic cytochrome C interacts with Apaf-1, which induces its association with procaspase-9, thereby triggering processing and consequent activation of caspase-9. The activated caspase-9 in turn cleaves downstream effector caspases (such as caspase-3), initiating apoptotic execution (Green et al., supra; Martin, et al., 1995, Cell. 82:349-52; Thomberry et al., 1998, Science. 281:1312-6). It is believed that activating effector caspases leads to apoptosis through the proteolytic cleavage of important cellular proteins, such as poly(ADP-ribose) polymerase (PARP) (Lazebnik et al., 1994, Nature. 371:346-7) and the retinoblastoma protein (RB) (An et al., 1996, Cancer Res. 56:438-42; Janicke et al., 1996, Embo J. 15:6969-78; Fattman, et al., 2001, Oncogene. 20:2918-26).
Activating the cellular apoptotic program is a current strategy for treating human cancer. In fact, radiation and standard chemotherapeutic drugs have been demonstrated to kill some tumor cells by inducing apoptosis (Fisher, 1994, Cell. 78:539-42).
Unfortunately, the majority of human cancers at present are resistant to present therapies (Harrison, 1995, J Pathol. 175: 7-12; Desoize, 1994, Anticancer Res. 14: 2291-2294; Kellen, 1994, Anticancer Res. 14:433-435). It is therefore essential to identify novel anti-cancer compounds that induce apoptosis. Along this line, synthetic small compounds have great potential to be developed into anticancer drugs because they can be easily synthesized and structurally manipulated for selective development.
For more than 60 years, N-thiolated β-lactam antibiotics have played an essential role in treating bacterial infections (Morin et al., Chemistry and Biology of beta-lactam Antibiotics, Vol. 1-3. New York: Academic Press, 1982; Kukacs et al., Recent Progress in the Chemical Synthesis of Antibiotics. Berlin, Springer-Verlag, 1990). Recently a new class of N-thiolated β-lactam is found to inhibit bacterial growth in Staphylococcus aureus (Turos et al., 2000, Tetrahedron 56:5571-5578; Ren, et al., 1998, J. Org. Chem. 63: 8898-8917). These compounds thus have proven clinical acceptability. To date, N-thiolated β-lactam compounds have not found use as anticancer drugs. Accordingly, N-thiolated β-lactam compounds that rapidly induce DNA damage, inhibit DNA replication, and induce an apoptotic effect, including inducing a death program of a neoplastic cell in a time and concentration dependent manner are desired.